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Topic: Is Solar power dirty? (Read 2089 times)

Hi, At my office we on almost done installing Solar. A few electrician iv talked to have mentioned that the power we will be feeding back into the grid would be "dirty power" I looked this up and it looks to be due to the DC to AC conversion and how some Inverters use more of a square wave and other inverters use a pulse width modulation. We are putting in 11 SMA Sunny Boy sb7.7-1sp-us-40 Inverters.

Using an oscilloscope is there a good way to see how clean the power is? Thanks.

You asked an electrician about an electronics question.He answered it based on his very limited understanding, and some anecdotes based on different topology inverters.The sunny boy 7.7 has less than 4% Harmonics according to the datasheet. So your power will be maximum 4% "dirty"

On the other hand I do know where virtually all the stuff we happily use on a day to day basis came from: China. And I know something else too. All that shit generated a lot of CO2 being produced for us and shipped to us for peanuts, and keeps generating CO2 while being used. Which cannot be said from solar panels, which produce CO2 free energy long after the first 6 to 12 months the average panel needs to return the energy involved in producing it.

Using an oscilloscope is there a good way to see how clean the power is?

You can use a DSO with a high-pass filter function. As you adjust the corner frequency up, the amplitude of the signal will decrease, until only the higher harmonics are left. By comparing the amplitude at any given corner frequency with a clean power signal, you can also quantify the low harmonics (which will increase the amplitude).You can also use the FFT function to convert the signal to the frequency domain. Harmonics (or sub-harmonics) will appear off the main power frequency (50 or 60 Hz). However, impulse noise is harder to see on FFT plot compared to the filter approach.

All the office equipment and lighting in your office is probably responsible for more dirty power than these inverters would supply. It is unlikely you will be able to see just how bad the utility power is now that the inverters are installed . Raw power doesn't need to be that clean. That is something marketing people thought up.

Using an oscilloscope is there a good way to see how clean the power is?

You can use a DSO with a high-pass filter function. As you adjust the corner frequency up, the amplitude of the signal will decrease, until only the higher harmonics are left. By comparing the amplitude at any given corner frequency with a clean power signal, you can also quantify the low harmonics (which will increase the amplitude).You can also use the FFT function to convert the signal to the frequency domain. Harmonics (or sub-harmonics) will appear off the main power frequency (50 or 60 Hz). However, impulse noise is harder to see on FFT plot compared to the filter approach.

Solar panels don't grow on trees. It takes energy to make a solar panel. Manufacturing solar panels has it's toll on the environment just like anything else. I often wonder if it takes more energy to make a solar panel than it will give out in its lifetime? Think of all the making, eating, pissing, shitting and rooting that's required to just get a panel on the roof, before it's even switched on. We live in a system of diminishing returns. No one ever considers the Total Energy Expenditure.Now where did I put my scrumpy?

Solar panels don't grow on trees. It takes energy to make a solar panel. Manufacturing solar panels has it's toll on the environment just like anything else. I often wonder if it takes more energy to make a solar panel than it will give out in its lifetime? Think of all the making, eating, pissing, shitting and rooting that's required to just get a panel on the roof, before it's even switched on. We live in a system of diminishing returns. No one ever considers the Total Energy Expenditure.Now where did I put my scrumpy?

Lots of people take the total lifecycle energy usage of these products very seriously. The snag is their figures seldom agree very well. Its pretty clear that the energy produced by solar panels exceeds the energy consumed for manufacture, deployment and support, as long as the system is kept deployed for a long time. However, by some measures the ratio might only be a few times as much energy produced. The casual observer, noting that these panels are designed to operate for at least 25 years, might expect a much higher multiple.

Everyone lies in the energy business. There's too much money involved for people to stay honest. Take all figures not presented with lots of solid supporting material with a pinch of salt. If there is supporting material, be highly suspicious of it, and probe its origins.

That said, I think the original post is actually referring to dirty power as in distorted power waveforms. Most approvable grid tie inverters are required to produce a fairly clean sine wave. It doesn't need to be perfect. The mains power is rarely that clean. Even a simple incandescent lamp causes 10% to 20% THD in its current waveform, due to the rapid heating and cooling of the filament through each half-cycle of the mains.

A few electrician iv talked to have mentioned that the power we will be feeding back into the grid would be "dirty power" I looked this up and it looks to be due to the DC to AC conversion and how some Inverters use more of a square wave and other inverters use a pulse width modulation.

You are somewhat correct. A grid with solely producers and consumers that have unfiltered inverters would be terribly "dirty" in terms of harmonics.It is easy to filter high frequency (>10KHz) "dirt" from mains by means of small inductor and capacitor.It is hard to filter low frequency (<10KHz). This is where line reactors and transformers, physical copper with magnetics, come in and filter harmonics.

Would putting several tens of microfarads directly across the output of a solar inverter help reduce any high frequency noise going out into the AC line?

Do you mean that putting some capacitors in parallel with the mains will clean-up the entire grid? I do not think that this works, because of low impedance and creating large inactive currents. I think this is performed before "pollution" reaches the output, by decoupling the output for high frequencies...